FIG. 1 shows a prior art milk measuring device (U.S. Pat. No. 2,998,722) Within containers 12, 13 are housed a separating chamber 16 for separating milk from the mixture of milk and air which has been milked from a cow and a measuring means 14 which is positioned beneath the separating chamber 16 and which repeats vertically revolving movements in correspondence to the flow rate. The milk mixture extracted by a milking machine is guided into an inlet port 15 provided on the top of the container 12 via a milk tube (not shown) and then into the separating chamber 16. The mixture of milk and air which has been directed into the separating chamber 16 is reduced in inlet energy by a rectifying plate 17 and the milk is directed to flow into the measuring means 14 through an outlet port 18 provided on the bottom of the separating chamber 16. The air separated from the milk passes through a narrow space 20 provided between the container 12 and the chamber 16 to arrive at an outlet port 21 on the bottom of the container 13, rejoins the milk which has passed through the measuring means 14 and is finally guided into a milk supply tube (not shown). The measuring device 14 comprises two tanks to temporarily store the milk which are journaled rotatively on an axis 14a fixed on the container 13. The measuring device 14 further comprises permanent magnets 19a on the bottoms of respective tanks. Magnets 19b are provided on the container 13 to correspond to the magnets 19a. When milk flows and stands in a tank in an amount which sufficiently overcomes the magnetic attraction between the magnet 19a of the other tank and the magnet 19b corresponding thereto, the weight equilibrium between two sides of the axis 14a breaks, to thereby lower the tank containing the milk around the axis 14a to the extent where the magnet thereof is attracted and attached to the other corresponding magnet. That makes the standing milk to flow out of the tank and meanwhile, the milk which is being milked continuously flows in to the other tank of the measuring means 14.
The total amount of milk can be measured by detecting the number of movements of the measuring means 14 which repeats the above mentioned movements and multiplying the number by the amount of milk which is to be discharged by one movement of the means 14.
The prior art device mentioned above, however, is detrimental in the following aspects:
As the measuring means 14 is structured with two tanks and as the position of the means 14 must be retained while milk is being filled in one of the tanks, the other tank must have a given retaining force which counter-balances the predetermined amount of milk in the first tank. In order to give such a retaining force, the suction of magnets is utilized. However, the magnetic force of magnets varies widely. Moreover, as the magnetic force changes suddenly in a manner counter-proportionate to the square of distance, it is necessary to mount a special mechanism for adjusting the magnetic force on the device so as to cause a pair of magnets to generate a predetermined suction force, presenting difficulties in cost and size of the prior art device.
As the magnetic force of a magnet undergoes chronological changes by various factors, it is extremely difficult to maintain the predetermined precision thereof for a long term without proper maintenance service. Even with periodical maintenance service, it is still difficult for users to adjust the device to the predetermined precision.
As the means 14 has two tanks, the size of the device per se becomes inevitably bulky presenting trouble in transportation while milking.
Another prior art measuring device as shown in FIGS. 11 and 12 has been known; wherein the filling time of milk into a measuring container and the discharging time thereof are measured (JAP Laid-Open No. Sho 57-18926). When a measuring chamber 55 is being filled with a valve 50 closed, the time Ci required for a float 53 to move from the lower magnetic sensor 51 to the upper magnetic sensor 52 is measured by the above two sensors. Within that time period, the volume V is filled in the chamber 55. After the float 53 has reached the sensor 52, a milk outlet port 54 is opened via the valve 50 and the float 53 goes down to the sensor 51 within the time di. Then, the valve 50 is closed and the float goes up again. Qi represents the average partial flow rate and is expressed by the equation, EQU Qi=(V/ci).
If it is assumed that the flow comes in within the time di at a predetermined average partial flow rate, the volume Vi which flows in within the time, bi=ci+di can be expressed as below; EQU Vi=Qi.times.x bi=(bi/ci).times.V
The total amount of the extracted milk which is measured by n times can be obtained from the equation; ##EQU1##
The prior art measuring method, however, is defective in that, as it is assumed that the milk which flows in within the time required for the liquid level to move from the upper sensor 52 to the lower sensor 51 supposedly flows at the average partial flow rate Qi of the filling time ci. In actual milking operation, the partial flow rate in the filling time does not necessarily coincide with the partial flow rate in the discharging time and therefore, a high precision in measuring can not be expected.